HaJo Geisler was an individual medley specialist. He won the bronze medal at the 1975 Cali World Championships in the 400 medley, where he also won the gold medal with the West German 4x200 m freestyle relay squad. He was also selected for the 400 medley at the 1972 München and 1976 Montréal Olympics. In München he was eliminated in the heats, and in Montréal finished eighth, and was also a member of the 4x200 m freestyle relay squad that was an unfortunate fourth, only 16/100 behind Great Britain. Between 1973-78 Geisler won six West German titles in the 400 m individual medley, was the 200 m medley champion in 1977, and in 1974 captured the national 1,500 m freestyle title.